The present invention relates to the reduction of vibration and noise by damping constructions, and particularly such damping constructions utilizing a layer of viscoelastic damping material. The invention has application to damping vibrations in vibrating or vibration generating systems, such as computer disk drive assemblies, automotive body panels, electronic cabinetry, or motor shrouds.
Vibrational energy or force is often transmitted from its source to another structure through a bolt, a screw or other connecting means which connects the vibrational source to the structure. In many applications this transmission of vibrational energy or force has a deleterious effect, often creating noise or excessive wear in critical components. Consequently, the ability to stop or reduce the transmission of vibrational energy or force is of great importance in certain applications.
For example, disk drive assemblies often require a relatively vibration-free environment to function optimally. The rotating parts of disk drive assemblies can inherently generate vibration and noise which, at certain levels, can degrade the performance of the drive assembly. Referring to FIG. 1, there is illustrated a portion of a prior art disk drive assembly 10 which has a spindle 11 having a fixed inner portion 12 and a rotating outer portion 13. The disk drive assembly housing has a cover 14 which is fastened to the inner portion 12 of the spindle 11, as by a screw 15. This construction permits vibrations to be mechanically coupled to the cover 14 through the spindle portion 12 and the screw 15.
To reduce the vibrations of the disk drive assembly, the arrangement of FIG. 2 was introduced. In this arrangement the head of the screw 15 passes through a hole 16 in the cover 14. The screw shank also passes through and engages a washer 17, known as a xe2x80x9cwhirlxe2x80x9d washer, and an overlying viscoelastic layer 18, which are interposed between the spindle portion 12 and the cover 14. The washer 17 may be formed of stainless steel, having a thickness in the range of from about 10 mils to about 20 mils, and the viscoelastic layer 18 may have a thickness of about 1-10 mils and could, if desired, be formed by a viscoelastic tape. The layer 18 serves to adhesively secure the cover 14 to the washer 17 which is, in turn, fixed to the spindle portion 12 by the screw 15. Thus, mechanical transmission of vibration from the spindle to the cover 14 is inhibited. The washer 17 and viscoelastic layer 18 serve to isolate the cover 14 from the spindle 11 at high frequencies and introduce damping into the system of the disk drive and cover assembly at lower frequencies.
Another approach is to damp any vibrations which do get transmitted into the cover 14, by applying to its outer surface a damping construction, which may be a constrained-layer arrangement including a metal skin having a viscoelastic polymer adhesive on one side thereof which is secured to the outer surface of the cover 14.
While these prior arrangements, particularly in combination, are effective in damping vibrations, they are relatively expensive to manufacture, involving assembly of a number of parts.
It is a general object of the invention to provide an improved vibration damping arrangement which avoids the disadvantages of prior arrangements, while affording additional structural and operating advantages.
An important feature of the invention is the provision of a damping arrangement of the type set forth, which is of relatively simple and economical construction.
Another feature of the invention is the provision of a damping arrangement which is adaptable for use in the covers of disk drive assemblies to introduce high damping and to isolate the cover from the mechanical transmission of vibration thereto from the drive assembly.